Orthogonal Polarization Suppression Ratio Research Articles

Stably polarized 795 nm vertical-cavity surface-emitting lasers with anti-phase SiNx surface gratings

795 nm vertical-cavity surface-emitting lasers (VCSELs) with dielectric surface gratings to control the output polarization are designed and fabricated. The calculated results demonstrate that a well-designed SiNx surface grating positioned on the surface of an anti-phase VCSEL structure enhances the reflectivity difference between the two polarization modes compared to a conventional GaAs surface grating, consequently resulting in a larger gain anisotropy in VCSELs and a high orthogonal polarization suppression ratio (OPSR). Characterization shows that a peak-to-peak OPSR of 30.3 dB is achieved at 85°C for 795 nm VCSELs with a SiNx surface grating of 5 µm in diameter and an oxide aperture of ∼4µm, demonstrating the effectiveness of the SiNx surface grating in polarization control for 795 nm VCSELs.

An InGaAs Vertical-Cavity Surface-Emitting Laser Emitting at 1130 nm for Silicon Photonics Application

A highly strained InGaAs quantum well (QW) vertical-cavity surface-emitting laser (VCSEL) with low threshold current density, high efficiency and output power emissions around 1130 nm was grown by MOCVD. Its static characteristics at room temperature and high operation temperature were studied in detail. The 7 μm oxide aperture device exhibits a threshold current of 0.68 mA, corresponding to a threshold current density of 1.7 kA/cm2. The slope efficiency is 0.43 W/A and the maximum output power is 3.3 mW. Continuous-wave (CW) operation in the 10–80 °C temperature range is observed. The slope efficiency is almost constant at 10–80 °C. The threshold current becomes lower at high temperatures thanks to the alignment between gain peak and cavity mode. The 3 μm oxide aperture device’s lasing in single mode with the RMS spectral width of 0.163 nm and orthogonal polarization suppression ratio (OPSR) is ~15 dB at 25 °C. The small-signal response analysis indicates that reducing the parasitics of the device and refining the fabrication process will improve the dynamics response characteristics. These results indicate that the 1130 nm GaAs-based VCSEL with highly strained InGaAs QWs is expected to be used as source for silicon photonics.

Polarization-stable single-mode 795 nm grating-coupled surface-emitting laser for quantum sensing

We demonstrate a polarization-stable and single-mode grating-coupled surface-emitting laser (GCSEL) with high side-mode suppression ratio (SMSR) of ∼40 dB and orthogonal polarization suppression ratio (OPSR) of ∼25 dB around 795 nm. The fabricated devices have low threshold current of ∼4.8 mA and low electrical resistance of 53 Ω at 25 °C. Meanwhile, a low thermal resistance of ∼1 K/mW is achieved, which is comparable with that of the record of ever reported for vertical-cavity surface-emitting lasers (VCSELs). The far-field divergence angle of surface-emitting beam is ∼14.5°x14.7° at an injection current of 12 mA indicating a relatively good beam quality. Our results open what we believe is a new way to produce polarization-stable single-mode surface-emitting lasers with simple fabrication process. While the GCSEL is specifically designed for quantum sensing applications such as atomic clocks, magnetometers, and gyroscope, its performance in terms of low-power consumption, low thermal resistance, good beam qualities, and wafer-level testing are of particular interest for a wide range of applications.

Surface-Emitting Lasers with Surface Metastructures

Vertical-cavity surface-emitting lasers (VCSELs) have been widely used in consumer electronics, light detection and ranging, optical interconnects, atomic sensors, and so on. In this paper, a VCSEL with the surface metastructure like one-dimensional high-contrast grating (HCG), based on the HCG-DBR vertical cavity, was first designed and fabricated. The polarization characteristic of the HCG-VCSEL were experimentally studied. The p-doped top 4-pair DBR for the current spreading and the direction shift between the HCG and the elliptical oxide aperture may result in a low orthogonal polarization suppression ratio in the HCG-VCSEL. Then, the Bloch surface wave surface-emitting laser (BSW-SEL), based on the HCG-DBR metastructure, is proposed for single-mode, high-efficiency, and high-power output with a low divergence angle. The mode field and the far field profile of the BSW-SEL are calculated for verification. The surface-emitting lasers with surface metastructures are useful for the sensing applications and optical interconnects.

Low Threshold Current and Polarization-Stabilized 795 nm Vertical-Cavity Surface-Emitting Lasers

Low threshold current and polarization-stabilized 795 nm vertical-cavity surface-emitting lasers (VCSELs) are fabricated by integrating a surface grating of high polarization selectivity and high reflectivity. The rigorous coupled-wave analysis method is used to design the surface grating. For the devices with a grating period of 500 nm, a grating depth of ~150 nm, and a diameter of the surface grating region of 5 μm, a threshold current of 0.4 mA and an orthogonal polarization suppression ratio (OPSR) of 19.56 dB are obtained. The emission wavelength of 795 nm of a single transverse mode VCSEL is achieved at a temperature of 85 °C under an injection current of 0.9 mA. In addition, experiments demonstrate that the threshold and output power also depended on the size of the grating region.

Mode characteristics of VCSELs with different shape and size oxidation apertures

Vertical cavity surface emitting laser (VCSELs) as the ideal light source for rubidium (Rb) and cesium (Cs) atomic clocks is analyzed for its mode and polarization control. We fabricated three kinds of shapes: triangular, elliptic, and circular oxidation apertures which also have different sizes. We formed three different shape oxide apertures by wet-oxidation with 36 μm–39 μm circular mesa. Our results show that triangular oxidized-VCSEL has the advantages of mode and polarization selection over elliptic and circular oxide apertures. When triangular oxide-confined VCSELs emit in single mode, the measured side mode suppression ratio (SMSR) is larger than 20 dB and orthogonal polarization suppression ratio achieves 10 dB. Resonant blueshift of VCSELs with triangular and elliptic apertures is observed with the decrease of aperture size.

Polarization control of 795 nm vertical-cavity surface-emitting lasers by in-phase surface gratings.

795 nm vertical-cavity surface-emitting lasers (VCSELs) with in-phase surface gratings are fabricated and investigated theoretically and experimentally. The polarization characteristics of 795 nm VCSELs with various grating periods and depths are analyzed using the rigorous coupled-wave analysis (RCWA) method; the dependence of polarization stability on the profile of gratings demonstrates that the trapezoid grating ridge slightly enhances the orthogonal polarization suppression ratio (OPSR), but increases the threshold current. The fabricated VCSELs with a sub-wavelength in-phase surface grating of a duty cycle of 0.5 show stabilized output polarization at the cost of increasing the threshold current which is in agreement with the calculations. The grating VCSELs with a period of 200 nm and an oxide aperture of 3.43µm×4.39µm produce a single-mode output with an OPSR of 16.6 dB and a slope efficiency of 0.42 W/A at 85°C.

Low-Noise, Single-Polarized, and High-Speed Vertical-Cavity Surface-Emitting Lasers for Very Short Reach Data Communication

A novel technique is demonstrated for suppressing the relative intensity noise (RIN) and enhancing the high-speed transmission performance of 850 nm vertical-cavity surface emitting lasers (VCSELs). The orthogonal polarization suppression ratio (OPSR) of top-emitting high-speed 850 nm VCSELs with rectangular shaped mesas can be greatly enhanced by electroplating a copper substrate onto the backside, without any degradation in slope efficiency (output power). The enhancement of the OPSR results in a significant reduction of the RIN (around −130 vs. −145 dB/Hz) over a wide frequency range (near DC to 20 GHz) in comparison to the reference device without the additional copper substrate. Moreover, the structure of the demonstrated device can not only flatten the electrical-to-optical (E-O) responses but also narrow the spectral width due to the strain induced by the copper substrate. Overall, the lower RIN and flatter E-O frequency responses in turn lead to a significant improvement in the 25 Gbit/sec eye-opening and lower timing jitter in our demonstrated device.

Polarization-pinning in substrate emission multi-mode vertical-cavity surface-emitting lasers using deep trenches

We investigated the stable polarization-pinning properties of substrate emission InGaAs-based 980 nm multi-mode vertical-cavity surface-emitting lasers (VCSELs). For the multi-mode 40 um diameter aperture VCSELs, we introduced 30 μm wide, 9 μm depth deep trenches that are 15 μm away from the cavity aperture. The VCSELs with trench structure produced higher transverse-electric (TE) polarized light output power, as compared with transverse-magnetic (TM) polarized light output power, namely, the effective TM polarization suppression was realized. These trench-etched VCSELs exhibited a 7.5 dB orthogonal polarization suppression ratio with 16.8 mW of light output power at 60 mA of current injection. The dominant TE polarization distribution was observed in polarization-resolved near-field images of spontaneous and stimulated emission due to the induced strain by the etched trenches.

A vertical cavity surface emitting laser for CPT atomic clock

A polarization-stabilized fundamental mode vertical cavity surface emitting laser (VCSEL) was developed for a coherent population trapping (CPT) Cs atomic clock. The VCSEL achieved a single stabilized polarization state through a directly-etched surface grating structure on the surface. The device polarization characteristics of different surface grating parameters were analysed using the finite-difference time-domain (FDTD) method. For the fundamental transverse mode condition, the lasing wavelength corresponded to the Cs atom’s D1 line. Owing to the polarization-dependent reflectivity of surface gratings, the VCSEL’s orthogonal polarization suppression ratio (OPSR) exceeded 20 dB. Since the surface grating eliminated the degeneracy of the two orthogonal linear polarization fundamental modes, a linewidth of approximately 53 MHz for the VCSEL could be obtained using the delayed self-homodyne method. A 7.6 GHz modulation bandwidth satisfied the atomic clock’s bandwidth requirement. We introduced the directly-etched surface grating VCSEL to the Cs atomic clock, and measured the CPT resonance signal.

Fabrication and Characterization of Low-Threshold Single Fundamental Mode VCSELs With Dielectric DBR Mirror

The SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> dielectric film stacks deposited by inductively coupled plasma chemical vapor deposition (ICP-CVD) are employed on the top of the oxide-confined vertical-cavity surface-emitting lasers (VCSELs). The reflecting mirror characteristics of the dielectric films are measured with varying numbers of pairs from 4 to 12. The prepared devices have low threshold current of 0.3 mA, single-mode peak power of 1.4 mW at room temperature. The thermal resistance of the device depending on ambient temperature is estimated according to the relationship of wavelength shift and dissipated power, allowing us to extract the actual temperature in active region and the temperature dependence of the output characteristics of the VCSEL. The beam property of the device is characterized by the far field pattern (FFP). Depending on the drive current, the average divergence angles of the output beam estimated from the full-width-half-maximum (FWHM) of the FFP varies between 20.4° and 21.2°. Furthermore, polarization-controlled single mode emission is achieved by introducing a built-in grating into the VCSEL with orthogonal polarization suppression ratio (OPSR) around 19 dB.

Asymmetric oxide apertures of vertical-cavity surface-emitting lasers fabricated by unsymmetrical wet oxidation and its polarization control

Given the high symmetry of vertical-cavity surface-emitting lasers (VCSELs) along their emission axis, these lasers demonstrate intrinsic polarization instability. In this study, we report the anisotropy oxide apertures of VCSEL formed by the unsymmetrical airflow distribution during the wet oxidation process. The polarization directions of VCSELs with anisotropy oxide apertures are well-controlled. VCSELs with oxide apertures of 2 μm × 4.6 μm achieve an orthogonal polarization suppression ratio of more than 20 dB and side-mode suppression ratio of more than 25 dB. In addition, an asymmetric far field distribution is observed, which can be ascribed to the asymmetric oxide apertures.

Polarization control and mode optimization of 850\xa0nm multi-mode VCSELs using surface grating

To control the polarization of 850 nm multi-mode oxide-confined vertical-cavity surface-emitting lasers (VCSELs), monolithically integrated surface gratings are investigated. VCSELs with different grating parameters are simulated by the rigorous coupled-wave analysis (RCWA) method. Optical field intensity of two polarization orientations with different grating periods and duty cycles is obtained. The mode characteristics of VCSELs with different grating parameters are achieved by FDTD method. 850 nm surface grating VCSELs are fabricated and characterized, a maximum orthogonal polarization suppression ratio (OPSR) of 20.7 dB is observed. Meanwhile, VCSEL’s output mode characteristics are improved by integrating the surface grating. Application of integrated surface grating technique to achieve dynamically polarization-stable multi-mode VCSELs which enable polarization division multiplexed data transmission, the data throughput over a given link can be doubled.

Polarization control and tuning efficiency of tunable vertical-cavity surface-emitting laser with internal-cavity sub-wavelength grating**Project supported by the Jilin Science and Technology Development Plan, China (Grant Nos. 20180519018JH and 20190302052GX), Jilin Education Department “135” Science and Technology, China (Grant No. JJKH20190543KJ), the National Natural Science Foundation of China (Grant No. 11474038), and the Key Project of Equipment Pre-Research Fund of China

We design an 850 nm tunable vertical-cavity surface-emitting laser (VCSEL) structure using an internal-cavity sub-wavelength grating. The use of such a tuning structure allows for wider wavelength tuning range and more stable single-polarization as compared to conventional tunable VCSELs. The features of the internal-cavity grating effect on the wavelength tuning and polarization characteristics of the tunable VCSEL are analyzed. The simulation results show that the largest wavelength tuning range achieves 44.2 nm, and the maximum orthogonal polarization suppression ratio (OPSR) is 33.4 dB (TE-type) and 38.7 dB (TM-type).

Polarization stabilized VCSELs by displacement Talbot lithography-defined surface gratings

Polarization-stable vertical-cavity surface-emitting lasers (VCSELs) with a simple fabrication process are presented. The gratings fixing the polarization are defined by a two-step exposure technology taking advantage of the displacement Talbot lithography technique. This enables grating lines to remain within the inner circle mesa of the VCSELs. These surface grating VCSELs with different periods are theoretically modeled and experimentally verified. Most of these VCSELs exhibit full polarization stability as predicted theoretically. For VCSELs with grating periods larger than the emission wavelength we found a weak orthogonal polarization suppression ratio, thereby deviating from those grating VCSELs with smaller periods.

Polarization-controlled and single-transverse-mode vertical-cavity surface-emitting lasers with eye-shaped oxide aperture

We presented a single-transverse-mode and single-polarization vertical-cavity surface-emitting laser (VCSEL) with an eye-shaped oxide aperture, obtained by enhanced anisotropic oxidation of oxide layer. For apertures with dimensions of 2 × 4.6 and 3 × 6 µm2, the orthogonal polarization suppression ratio (OPSR) of the VCSEL was 22 and 19 dB, respectively. A single-mode suppression ratio (SMSR) of more than 25 dB at an output power of 0.5 mW was also achieved for the VCSEL with aperture dimension of 2 × 4.6 µm2. We believe that the proposed method to realize the mode and polarization control of VCSELs has great potential in future applications.

VCSEL mode and polarization control by an elliptic dielectric mode filter.

In this paper, we demonstrate the effectiveness of polarization mode control in vertical-cavity surface-emitting lasers (VCSELs) with integrated elliptic dielectric mode filters. The single-mode single-polarization laser operation is obtained by an irregularly shaped oval dielectric mode filter, aimed at cost-effective mass production. The orthogonal polarization suppression ratio was measured to be 16.7 dB, and the side-mode suppression ratio exceeded 30 dB. A single fundamental mode power of 0.55 mW was achieved at a bias current of 4 mA. We compared the spectra and near-field intensities of the dielectric mode filter VCSEL with a reference device. The comparison clearly indicates the effectiveness of our dielectric mode filter in controlling the transverse- and polarization-mode properties of VCSELs.

Laser Source for a Compact Nuclear Magnetic Resonance Gyroscope

Vertical-cavity surface-emitting lasers (VCSELs) of 895 nm spectral range, with fixed direction of output polarization have been developed. These lasers provide single-mode output power of over 1 mW at an operational temperature of 60°С, at orthogonal polarization suppression ratio (OPSR) about 20 dB. The designed VCSELs were used in a laser source for a perspective compact nuclear magnetic resonance gyroscope. The designed laser source provides precise tuning of wavelength to the Cs133 D1 spectral line, and formation of collimated output beam.

OPSR enhancement of high-temperature operating shallow-surface grating VCSELs.

A polarization-stable single-mode 894nm vertical cavity surface emitting laser (VCSEL) with an orthogonal polarization suppression ratio of 30dB, even at a temperature up to 80°C, was achieved for atomic clock applications by utilizing shallow-surface gratings. An improved grating VCSEL fabrication technology for mass production was also proposed by taking advantage of the displacement Talbot lithography. The multi-mode grating VCSEL was also measured for other applications that need polarization stability, such as doubled-data-rate polarization multiplexed free-space links.

Polarization Stable Vertical Cavity Surface Emitting Laser Array Based on Proton Implantation**Supported by the National Natural Science Foundation of China under Grant Nos 61376049, 61076044, 61107026 and 61204011, the Natural Science Foundation of Beijing under Grant Nos 4132006, 4102003 and 4112006, the Scientific Research Fund Project of Municipal Education Commission of Beijing under Grant No PXM2013-014204-000029, and the Specialized Research

Polarization stable characteristic of vertical cavity surface emitting laser array with rectangular element structure based on proton implantation is achieved. Arrays with different aperture sizes and different array scales are investigated. The maximum orthogonal polarization suppression ratio of a 6 × 6 array with 6 μm; × 4 μm elements is as high as 16.1 dB at 51 mA. The x-polarization dominates y-polarization in the operation current range from the threshold to the saturated current. The full widths at half maximum in far-field profiles for x-polarization and y-polarization are 8.8° and 10.7°, respectively. These results suggest that stable polarization is available in the implant-defined VCSEL array.